| Summary: | 碩士 === 國立中正大學 === 物理系研究所 === 105 === A series of magnetic multilayered structures are fabricated by sputtering and the current induced magnetization switching by spin Hall effect is studied in this thesis. The samples include: Si(substrate)/Ta(10)/MgO(1)/CoFeB(x)/W(1)/CoFeB(1.1)/MgO(1)/Ta(3), x= 1.2, 1.3,1.4 (units are nanometer). All samples are characterized by vibrating sample magnetometer (VSM) and the one with x= 1.4 is also measured by Hall resistance measurements.
The anomalous Hall resistance (Rxy) measurements include the current scan Rxy(I) and field scan Rxy(H), respectively. Note that the Rxy(I)(Rxy(H)) is measured as function of a fixed field (fixed current) and all these results are then mapped to a comprehensive phase diagram. The main interests focus on the current scan Rxy(I). However, the analysis starts with Rxy(H) because these results provide useful information on the relevant magnetic states which help to for clarify the role of the spin current and symmetry of the trilayered structure.
The experimental results of sample x=1.4 has two parts:
1.The characterization of VSM: the effective film thickness of the top CoFeB is 0.639 nm and bottom CoFeB is 0.503 nm. The total dead is 1.358nm.The magnetization of the multilayer is 1625emu/cm3, the anisotropy field is 4000 Oe, and the switching field is 300 Oe
2. The results of anomalous Hall resistance measurements are further divided in to three parts:
A. Rxy(Hz):
We measured Rxy(Hz) in range ±2000 Oe,and ±18 mA. The magnetic states change by applying different amplitude of currents. From field-current (H,I) diagram, the positive direction and the negative direction of currents have the same result, and thus we can infer the field like torque is the mainly effect in Rxy(Hz). We can also find the c-state and v-state in the ±15mA in the diagram and only c-state when current is over than ±15mA in the diagram.
B. Rxy(H_(83°)):
We found in the Rxy(H_(83°)) the current would generate the opposite field on the upper and the bottom magnetic layers. If the effective field along the z-axis induced by the current can cancel out the anisotropy field then the field like torque and antiparallel coupling may let the magnetic moments align to the hard axis which is called spin flop state or v-state. By applying〖 H〗_(83°)field from +2000 Oe to -2000 Oe we were able to see the magnetic state passing through 0.2 Ω (c-state) first, then go to the state near 0 Ω (v-state). In this process both damping like torque and field like torque exert on the top and bottom CoFeB layers.
C. Rxy(I):
We measured Rxy(I) in the range of ± 20 mA and ±2000 Oe. By current scaning in the range of -100 Oe < H < - 20 Oe , the magnetic reversal trace is from the state of 0 Ω (v-state) then go to the state of 0.2 Ω (c-state) as current sweeps from positive to negative and vice versa as the current sweeps from negative to positive. In addition, the current induced magnetization switching occurs at zero field, indicating that the in-plane symmetry is intrinsically broken by the spin current during the switching process. However, the symmetry center shifts to Hx= -60 Oe. From current-field (I, Hx) diagram, the switching can be divided into two regions. The inner region has two switching modes and the switching slope for the c-state is much sharper than the slope in the outer region.
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